The present invention relates to mounting and electrically connecting integrated circuits and, more particularly, to the packaging of an integrated circuit die in a high density multichip package.
Hybrid circuits involve a technology in which some elements are fabricated in film layers directly on a substrate material and other elements are discrete add-on-components. A typical hybrid circuit may be hermetically sealed within a protective package and may comprise a plurality of densely arranged integrated circuit chips. Several different approaches are used to make the input/output connections to the connection pads on the face of each tiny integrated circuit die.
One interconnection method is the so-called HDMI, or high density multichip interconnection, technique. In one HDMI process, the HDMI interconnect is built up layer by layer on a silicon or ceramic substrate, and the densely arranged integrated circuit chips are next bonded face-up to the HDMI substrate. Finally, the chips are connected electrically to the HDMI interconnect by wire bonding or by Tape Automated Bonding (TAB); both well known processes.
Another interconnection method is the so-called flip chip technique. One specific example of flip chip bonding is the process that is sometimes referred to as the C4 process. A flip chip is an integrated circuit die prepared for reflow face bonding by the growth of solder hemispheres on the bond pads of the chip. In the flip chip interconnection process, after the die has been prepared with solder bumps on its face, it is flipped over for attaching to a matching rigid substrate on which interconnecting thin films have previously been deposited. All connections are then made by applying heat.
Another technique for face down bonding to the bond pads is referred to as flip TRB, or testable ribbon bonding. A conductive connector ribbon having a kink for stress relief is used in place of the solder bumps. A die having the kinked ribbons is flipped over and attached to a mating rigid substrate on which interconnecting thin films have previously been deposited.
In conventional high density multichip packages, an integrated circuit die is typically mounted on a substrate made of a material that is not a good conductor of heat. Hence, the integrated circuit die is only partially cooled from the back side. Typically, the heat escapes by radiation from the cover of the package that encloses the chip and thus it is difficult to keep the package cool. As the chip density increases, it becomes more important to find ways to remove the heat from the integrated circuit package to keep the chips as cool as possible.
Accordingly, it is an objective of the present invention to provide a mounting and interconnection method that permits a direct thermal connection from an integrated circuit chip to a heat sink in a high density multichip package. Another objective of the present invention is to interconnect a flip chip die in a high density package without the strain of a rigid substrate.